1. Field of the Invention
The present invention relates to an engine of relatively small size for use, for example, as an engine for an outboard engine structure. The present invention further relates to an outboard engine structure having a small engine.
2. Description of the Prior Art
An outboard engine is disclosed, for example, in Japanese Patent Application Laid-open No. 267561/87. This engine includes a crankshaft disposed vertically, and two banks of cylinders disposed in an opposed V-shaped configuration. Each of the banks includes a cylinder block having three horizontal cylinders disposed in line along an axis of the crankshaft, and a cylinder head secured to an end face of the cylinder block in an axial direction of the cylinders.
Intake ports are located on the inner sides of the V-shaped banks. Intake pipes connected to the intake ports extend in a direction away from the crankshaft at least partially along a center line of the angle of the V formed between the banks. A multi-barrel, single-chamber carburetor is provided for every pair of opposed cylinders.
Exhaust ports are located on the outer sides of the banks. Exhaust passages connected to the exhaust ports, extend toward the crankshaft at least partially along the axes of the cylinders, and then extend to meet together in a single exhaust pipe.
In such a prior art engine, an intake system including the intake pipes and carburetors, is disposed on the inner side of the V-shaped banks. Therefore, it is difficult to reduce the angle formed between the banks arranged in the V-shape for decreasing the width of the engine, to thereby reduce the size of the engine.
Further, to reduce the angle of the V between the banks, the carburetor would have to protrude away from the crankshaft. This results in the problem that the length of the engine is increased, and the center of gravity of the engine itself is correspondingly displaced in a direction away from a crank chamber, which is not preferred depending upon conditions.
There is another conventionally known multi-cylinder engine intake device. In such a device, the same number of intake pipes as that of cylinders extend from a surge tank having a predetermined capacity, and the intake pipes are connected to intake ports. A fuel injection device is disposed in each of the intake ports or in each of the intake pipes in the vicinity of the intake port, and a throttle valve is mounted on the surge tank for controlling the amount of air drawn into the tank.
Such an intake device is disclosed, for example, in Japanese Patent Application Laid-open No. 60024/93. This intake device is applied to an in-line 4-cylinder engine for an outboard engine structure, and includes a surge tank disposed on one of the sides of the engine body at a location close to a crankcase. Four intake pipes (the same number as that of cylinders) extend from the surge tank and are connected to intake ports in a cylinder head, respectively.
The upper three of the four intake pipes extend upwardly from the side of the surge tank and are then curved downwardly at their intermediate portions. The remaining lowermost intake pipe extends straight laterally and downwardly from a bottom of the surge tank. All of the intake pipes are disposed to extend along the side of the engine body.
In such an engine, all the intake pipes extend from the single surge tank, and the total amount of air drawn must be provided by the single surge tank. Hence, the capacity of the surge tank is necessarily increased.
As a result, if the capacity of the single surge tank is increased, it is difficult to accommodate the surge tank in an engine compartment in a compact manner.
Therefore, there is almost no space for disposition of auxiliaries around the engine, resulting in a decreased degree of freedom for selection of positions for the disposition of the auxiliaries.